1. Field of the Invention
The present invention pertains to methods and apparatus which utilize an LCD modulator array for printing and/or enlarging an image recorded in a color film negative, a positive transparency, a color print or electronically.
2. Description of the Prior Art
A full color printer and/or enlarger which utilizes an LCD modulator array for printing and/or enlarging an image recorded in a color film negative, a positive transparency or a color print must scan the color film negative a number of times to acquire information about the images' chromanance and density. For example, once for each of three colors, to obtain a density value which is associated with each pixel (picture element) of the LCD modulator array. In practice, the scan time required to perform each scan can be quite long because of the response times of typical liquid crystal materials used in LCD modulator arrays. For example, FIG. 1 shows a response time curve for a typical LCD material. As one can readily appreciate, the "opening time" of a pixel in the LCD modulator array, i.e., the time it takes for the pixel in the LCD modulator array to convert from a state where less than or equal to about 1% of the radiation incident thereupon is transmitted to a state where over 90% of the radiation incident thereupon is transmitted, is typically about 0.1 ms and the "closing time" of the pixel in the LCD modulator array, i.e., the time it takes for the pixel in the LCD modulator array to convert from a state where over 90% of the radiation incident thereupon is transmitted to a state where less than or equal to about 1% of the radiation incident thereupon is transmitted, is typically about 20 ms. to 30 ms. Consequently, if one were to utilize even a coarse 64.times.64 pixel LCD modulator array in a printer and/or enlarger, the total opening time for the pixels of the LCD modulator array during each scan would be approximately 4 seconds and the total closing time for the pixels during each scan could be several minutes. Thus, a typical LCD modulator array utilized in a mode in which each pixel is opened and closed before the next succeeding pixel is opened and closed during each scan results in an extremely slow printer and/or enlarger.
Another additional problem associated with the use of an LCD modulator array for printing and/or enlarging an image recorded in, for example, a color film negative occurs because the pixels in an LCD modulator array are not completely opaque, even when completely closed. Specifically, because each pixel in a typical LCD modulator array is a leaky polarizer, an opacity problem occurs when an LCD modulator array is utilized for printing and/or enlarging. This opacity problem can be understood by considering a typical case where a closed pixel leaks about 1% of the radiation incident thereupon. For such a case, if the pixels of a 4000 pixel LCD modulator array were exposed, one at a time, for each of the three colors required to make a full color print, this would produce an unmodulated background exposure about forty times as great as the exposure which results from opening and closing a single pixel at any given time. Such a modulator would be almost ineffectual in varying the exposure locally in the print.
As one can readily appreciate from the above, there is a need in the art for method and apparatus which utilize an LCD modulator array for printing and/or enlarging an image recorded in a color film negative, a positive transparency, or a color print, which method and apparatus: (a) operate rapidly; (b) utilize an LCD modulator array which is comprised of pixels whose closing time plus opening time is approximately 30 milliseconds; and (c) achieve a modulation ratio of 10:1 (adequate for dodging applications) to 100:1 (adequate for printing a photograph from electronically stored information).